The backlight module as one of the important components in a liquid crystal display provides sufficient brightness and uniform distribution to enable the liquid crystal display present proper image, since liquid crystals do not emit lights on its own. At present, the display techniques for the liquid crystal display have already matured, in particular the design of the backlight module has made a great development. The backlight module can also be used to provide illumination for display devices such as digital photo frame, e-paper, cell phone and so on in addition to liquid crystal display device such as liquid crystal monitor, liquid crystal television and so on.
The backlight modules are categorized into a direct type backlight module and a side type backlight module according to the position of the light source. In the direct type backlight module, the light sources are placed below light emitting surface of the light source. The lights from the light sources travel through a certain distance and are diffused and blended by a diffuser plate, then the lights are emitted, acting as a surface light source. In the side type backlight module, the light sources are generally arranged on at least one of the side surfaces of the light guide plate. Lights are introduced into a light guide plate from the side surface and are subjected to a total reflection and continue to travel forward within the light guide plate. The lights are emitted out of the light guide plate by breaking the total reflection condition at the light emitting surface of the light guide plate. Hence, the configuration of the light guide plate has a primary influence on the light emitting effect of the backlight module.
FIG. 1 is a structural schematic view showing a conventional light guide plate. The light guide plate comprises a light guide plate substrate 9. The light guide plate substrate 9 comprises an incident surface 1 for receiving beams, a lower surface 3 jointed with the incident surface 1, an emitting surface 2 jointed with the incident surface 1 and opposing the lower surface 3, a side surface 4 opposing to the incident surface 1, and other two side surfaces opposing to each other. In order to break the total reflection of lights within the light guide plate, optical grid points 5 are provided at the lower surface 3. The lights entering the light guide plate are subjected to the total reflection on the inner sides of the light guide plate many times, and spread into the entire interior of the light guide plate. When the lights are diffused on the optical grid points 5 and emitted out of the light guide plate through the emitting surface 2 thereof (the lower surface 3 does not transmit lights). By adjusting the density of the optical grid points 5, the light guide plate can have an uniform light distribution across the entire emitting surface. A light source 6 is provided on the outer side of the incident surface 1. A reflective cover 7 is provided on outer side of the light source 6 and the side surface 4 and other side surfaces are formed as reflective by disposing reflective sheets. The lights emitted by the light source 6 enter the light guide plate through the incident surface 1, and emit out from the emitting surface 2 by the reflection of the lower surface 3 and side surface 4.
It is noted that the above light source can be positioned on at least one side surfaces of the light guide plate. The light source herein is only provided at one side surface of the light guide plate and for convenience of description. The above light guide plate in the backlight module used in a single side display device can only emit lights from a single emitting surface, and is unable to meet the requirements of a double-side display device.